In U.S. Pat. No. 5,030,890 entitled "Two Terminal Incandescent Lamp Controller", issued Jul. 9, 1991, there are disclosed and claimed new and useful improvements in the field of controlling various lighting functions of an incandescent lamp bulb, such as timing, duty cycle control, dimming and illumination intensity. This two terminal incandescent lamp controller is operative to provide in memory certain data values corresponding to the timing or sequence at which power interruptions to the memory may occur. Timed or sequenced power interruptions to the memory are created in order to select a particular data value for storage in memory which is then operative to control either the conduction time, the duty cycle, or the illumination intensity of the lamp bulb. This conduction time, duty cycle, or illumination intensity control is achieved by connecting an AC triggerable switch, such as a triac, to the lamp and controlling its conductive state by the application thereto of the particular data value selected for storage in the memory of a microprocessor or a microcontroller.
In a subsequent commonly assigned U.S. Pat. No. 5,126,634 entitled "Electronic Control Module (ECM) for Controlling Lighting Functions of a Lamp Bulb and Method of Manufacture" there are disclosed and claimed further new and useful improvements in the field of lamp bulb function control. These improvements include, among other things, a new and improved process for manufacturing an integrated circuit controlled light bulb. This manufacturing process includes the steps of providing a light bulb having a filament wire therein and a dielectric insulator at one end of the bulb, with the insulator having a recessed cavity adjacent to which an opening extends to an interior section of the bulb. An electronic control module (ECM) is mounted in this receptacle and then connected to a filament wire of the bulb for thereby controlling one or a plurality of bulb lighting functions in response to the operation of the electronic control module.
In yet a subsequently filed and commonly assigned U.S. application Ser. No. 07/847,179 entitled "Lamp Bulb With Integrated Bulb Control Circuitry and Method of Manufacture", filed Mar. 9, 1992, now U.S. Pat. No. 5,214,354, there are disclosed and claimed yet still further new and useful improvements in the field of electronic control module design wherein a new and improved ECM article of manufacture is constructed having a metal housing with a base or floor member being surrounded by an upstanding wall member defining an opening in the housing. A ceramic substrate is mounted on the base member, and bulb lighting control circuitry is constructed on the substrate and has a conductive bridge member connected thereto for transmitting control signals from a microprocessor or microcontroller in the bulb lighting control circuitry to the filament of a light bulb. This application and the above two patents preceding it are incorporated herein by reference.
Whereas the above identified inventions represent most significant advances in the fields of lamp bulb manufacture and associated lighting function control, the operation of the triac in the ECM module in response to the microprocessor or microcontroller can, in some cases, generate undesirable radio frequency interference (RFI) radiation. This RFI is generated as a result of the steep di/dt rise time due to the triac turn-on from voltage on each one-half cycle of the AC line which is applied across the anode and cathode terminals of the triac. This undesirable radio frequency interference can be radiated as RF signals from the lamp bulb acting as an antenna and into the surrounding ambient, and it can also be transmitted directly back through the AC line voltage source to thus provide electrical interference to other appliances connected to this same source of AC voltage. In either case, this radio frequency interference is undesirable and may in some cases exceed acceptable electrical and health code levels for RFI in certain countries.
The electrical and health code which governs acceptable levels of RFI define maximum allowable magnitudes of radiated and conducted RFI relative to the frequency at which the RFI is radiated. Conducted RFI will propagate back through the system wiring, which may be several tens of kilometers. This long length of wiring thus forms a very efficient transmitter of RFI. Also, it is much easier for conducted RFI to enter sensitive electronic equipment through a plug-in power cord. The relative magnitude of the radiated RFI is important because the strength of the RFI is directly related to the potential risk. However, higher frequency RFI can be radiated over greater distances and will achieve greater penetration than the RFI radiated at relatively lower frequencies. Consequently, the risk associated with RFI relates to both the magnitude of the RFI and the frequency at which the RFI is generated. Accordingly, the electrical code establishes different maximum RFI levels at different frequencies. At higher frequencies, the maximum allowable RFI levels are of lower than the maximum allowable RFI levels at lower frequency levels.
Conventional dimmer control devices are a source of conducted RFI. Dimmers are usually used with lighting and other devices to control the intensity of light or some other aspect of operation of the device which the dimmer controls. These dimmers usually include some type of controllable switch, such as a SCR or triac, which conducts current to the light or other device in a controllable manner by turning on and off almost instantaneously. This type of switching results in abrupt or step waveform of current conducted by the light or the device which is controlled. Measured di/dt values of this step are greater than 10.sup.7 amperes per second. The inherent characteristic of such step waveforms is the generation of a variety high frequency signals of varying magnitudes. In fact, the step waveform is a composite of signals of generally increasing frequencies and diminishing magnitudes.
Conventional dimmers often include filters to diminish the magnitude of the switching signals which cause RFI. Since dimmers are typically intended to permit operation with a variety lights and devices of different power ratings, the filtering capability must accommodate a relatively wide range of different loads. In order to accommodate the range of different loads, the filter may be incapable of sufficiently suppressing RFI when the dimmer is lightly loaded and allowed to resonate.
It is with respect to these considerations and other background information relative to lighting devices having light function control circuitry that the significant improvements of the present invention have evolved.